Proton conductivity in multi-component ABO4-type oxides†

This work investigates how configurational entropy in oxides could affect proton conductivity. For this purpose, three samples of different elemental compositions are synthesized. Five, six and seven elements were introduced into the A-site of ANbO₄, forming La_1/5 Nd_1/5 Sm_1/5Gd_1/5 Eu_1/5NbO₄, La_1/6Nd_1/6Sm_1/6Gd_1/6Eu_1/6Ho_1/6NbO₄ and La_1/7Nd_1/7Sm_1/7Gd_1/7Eu_1/7Ho_1/7Er_1/7NbO₄, respectively. The high configuration disorder changes the local environment, which can have a notable effect on many properties, including proton transport, which is the focus of this work. The conductivity was measured in different atmospheres; dry and wet and in a different temperature range (600–800 °C) to compare the proton transport as well as study the effect of temperature. A homogenous single-phase monoclinic fergusonite was obtained for the three samples. Proton conductivity, measured by means of comparing the conductivity in dry and wet atmospheres, was observed in all samples. La_1/5 Nd_1/5 Sm_1/5Gd_1/5 Eu_1/5NbO4 exhibited the highest conductivity, about 3.0 × 10⁻⁶ S cm⁻¹ at 800 °C in the wet atmosphere, while in the dry atmosphere it was about 2.2 × 10⁻⁶ S cm⁻¹ at the same temperature, which implies a modest proton conductivity in this class of materials.